Normally innocuous battle for state comptroller is seen as a proxy fight between Republican governor and Democratic state House speaker

CHICAGO—A surge in campaign spending has filtered down to one of the more obscure races here, making the normally innocuous battle for comptroller among the most expensive campaigns ever for a state office in Illinois.

The winner gets the pleasure of writing checks in a state that is almost $10 billion in the hole and muddling through the worst budget crisis in its history. The previous comptroller, who died shortly after winning...